Pneumatic tire and method of manufacturing the same

ABSTRACT

A pneumatic tire capable of eliminating the need of repairing puncture on the outside of a car and effectively preventing air leakage without accompanying an increase in weight and deterioration of riding comfortableness which occur in a conventional punctureless tire and a method of manufacturing the pneumatic tire, the pneumatic tire characterized in that a rubber-like thin-film formed of a latex dry thin-film in which 20 to 50 wt % rubber component is liquid isoprene rubber and having a breaking elongation of 900% or more and a tensile strength of 15 MPa or higher is disposed on the inner surface of the tire.

TECHNICAL FIELD

The present invention relates to a pneumatic tire suitable as aso-called punctureless tire. More specifically, the present inventionrelates to a pneumatic tire having an excellent puncture preventionfunction while eliminating disadvantages of a conventional puncturelesstire and relates to a method of manufacturing the same.

BACKGROUND ART

Various technologies have heretofore been proposed as measures againstpuncture. A run-flat tire, for example, includes thick cushion rubberfrom a tread portion to sidewall portions, and the run-flat tirepunctured allows driving about several hundred kilometers. However, oncepunctured, the run-flat tire cannot be repaired and reused. Moreover,the run-flat tire has a disadvantage that riding comfortableness innormal driving is impaired.

Another measure is a puncture repair liquid, which is a liquid repairagent and injected into a tire after the tire is punctured. The agent isthen solidified and fills a hole. Such a puncture repair liquid isversatile and easy to use, but requires a work on the outside of a carwhen the tire is punctured. The puncture repair liquid is thereforeunsuitable for use on a highway and the like.

Still another measure is a sealant tire in which a sealant (viscouscomposition) is previously disposed on the inner surface of the tire andautomatically fills a hole formed when the tire is punctured (forexample, see Japanese patent application Kokai publication No. Sho 53(1978)-55802). However, in the sealant tire, it is required to dispose athick sealant in order to obtain a sufficient effect. Thus, there is adisadvantage of an increase in weight. When the sealant is applied tothe inner surface of the tire, it is required to remove a mold releaseagent attached to the inner surface of the tire. Thus, productivity isalso poor.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a pneumatic tirecapable of eliminating the need of repairing puncture on the outside ofa car and effectively preventing air leakage without accompanying anincrease in weight and deterioration of riding comfortableness whichoccur in a conventional punctureless tire and to provide a method ofmanufacturing the pneumatic tire.

A pneumatic tire of the present invention to achieve the foregoingobject is characterized in that a rubber-like thin-film is disposed onan inner surface of the tire, the rubber-like thin-film being formed ofa latex dry thin-film in which 20 to 50 wt % rubber component is liquidisoprene rubber and having a breaking elongation of 900% or more and atensile strength of 15 MPa or higher.

As described above, the rubber-like thin-film with a large breakingelongation and a large tensile strength is disposed on the inner surfaceof the tire. Accordingly, when a foreign object such as a nail entersinto the tire or is removed from the tire, the rubber-like thin-filmaround a puncture hole can prevent air leakage. Moreover, the pneumatictire including the rubber-like thin-film described above is notaccompanied by an increase in weight and deterioration of ridingcomfortableness and eliminates the need of repairing puncture on theoutside of a car.

The latex dry thin-film includes properties as described above and canbe formed on the inner surface of the tire even in a state where a moldrelease agent is attached to the inner surface of the tire. Use of thelatex in which 20 to 50 wt % rubber component is liquid isoprene rubber,in particular, makes it possible to give optimal adhesion andstretchability to the rubber-like thin-film, and to exert an excellentpuncture prevention function for a foreign object having a thick andcomplicated shape such as a screw. Here, it is preferable that amolecular weight range of the liquid isoprene rubber is 20,000 to40,000.

In the present invention, in order to prevent the increase in weight, itis preferable that a thickness of the rubber-like thin-film is 2.0 mm orless. In the case where the mold release agent is interposed between therubber-like thin-film and the inner surface of the tire, the rubber-likethin-film is easily peeled off from the inner surface of the tire whenthe foreign object such as a nail enters into the tire. Accordingly, theair leakage can be prevented more effectively.

A method of manufacturing the pneumatic tire of the present inventionutilizing the above-described characteristics of the latex is a methodof manufacturing a pneumatic tire including a rubber-like thin-film onan inner surface of the tire, the rubber-like thin-film having abreaking elongation of 900% or more and a tensile strength of 15 MPa orhigher. The method is characterized by including: pouring latex in which20 to 50 wt % rubber component is liquid isoprene rubber into the tirevulcanized; and drying the latex while rotating the tire to form therubber-like thin-film composed of a dry thin-film of the latex on theinner surface of the tire. According to the manufacturing method asdescribed above, it is possible to easily form the rubber-like thin-filmwith a uniform thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a meridian half sectional view showing a pneumatic tireaccording to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state where a nail sticks ina tread portion.

FIG. 3 is a cross-sectional view showing a state after the nail isremoved from the tread portion.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the accompanying drawings, a constitution of thepresent invention will be described in detail below.

FIG. 1 shows a pneumatic tire according to an embodiment of the presentinvention. Reference numerals 1 to 3 denote a tread portion, a sidewallportion, and a bead portion, respectively. A carcass layer 4 is laidbetween the bead portion 3 and another bead portion 3 on the other side,and each end of the carcass layer 4 is folded around a bead core 5 fromthe inner side of the tire to the outer side of the tire. On the outerperipheral side of the carcass layer 4 in the tread portion 1, aplurality of belt layers 6 are buried.

In the above-described pneumatic tire, a rubber-like thin-film 7 with abreaking elongation of 900% or more, preferably, 900 to 1500%, and atensile strength of 15 MPa or higher, preferably, 15 to 20 MPa, isdisposed with a thickness of 2.0 mm or less in an area of an innersurface of the tire corresponding to the tread portion 1. Therubber-like thin-film 7 may be disposed not only in the area of theinner surface of the tire corresponding to the tread portion 1 but alsoin an area of the inner surface of the tire corresponding to thesidewall portion 2 and the bead portions 3.

When a foreign object such as a nail 11 sticks in the tread portion 1and enters into the tire, as shown in FIG. 2, the rubber-like thin-film7 described above is peeled off from the inner surface of the tire andclings to the foreign object such as the nail 11 to prevent air leakage.When the breaking elongation and the tensile strength of the rubber-likethin-film 7 are insufficient, the nail 11 or the like entering into thetire easily penetrates the rubber-like thin-film 7. Thus, a punctureprevention function does not work adequately.

On the other hand, when the foreign object such as the nail 11 isremoved, as shown in FIG. 3, the rubber-like thin-film 7 covers apuncture hole 12 and prevents air leakage. When the foreign object suchas the nail 11 is removed, in particular, the rubber-like thin-film 7clinging to the foreign object is bunched up into a ball to effectivelycover the puncture hole 12.

When a thickness of the rubber-like thin-film 7 exceeds 2.0 mm, a weightof the tire is significantly increased, and characteristics of the tireare changed, which is not preferable. It is preferable that a lowerlimit of the thickness of the rubber-like thin-film 7 is 0.1 mm, and thethickness thereof is selected within a range of 0.1 to 2.0 mm.

The rubber-like thin-film 7 is formed to have a uniform thickness bypouring latex having fluidity arbitrarily controlled into a normalproduct tire and drying the latex while gradually rotating the tire. Asfor the latex, it is necessary to use latex in which 20 to 50 wt %rubber component is liquid isoprene rubber. Here, it is preferable thata molecular weight range of the liquid isoprene rubber is 20,000 to40,000. Such liquid isoprene rubber increases tack of the rubber-likethin-film 7. When the liquid isoprene rubber is less than 20 wt % of therubber component, the tack of the rubber-like thin-film 7 isinsufficient. Accordingly, air leakage could be caused, for example,when a screw sticks in the tire. On the contrary, when the liquidisoprene rubber exceeds 50 wt % of the rubber component, elasticity ofthe rubber-like thin-film 7 is reduced, leading to inadequatesealability. The other rubber component of the latex is, preferably,natural rubber latex but may be synthetic rubber, such asstyrene-butadiene rubber (SBR), emulsified and dispersed in water.Moreover, in the latex rubber, a filler such as carbon black and variouscompounding ingredients may be added when needed.

When the rubber-like thin-film 7 is composed of a latex dry thin-film,it is not required to remove a mold release agent used in vulcanizationfrom the inner surface of the tire. In the case where the mold releaseagent is interposed between the rubber-like thin-film 7 and the innersurface of the tire, the rubber-like thin-film 7 is easily peeled offfrom the inner surface of the tire when the foreign object such as thenail enters into the tire. Thus, the air leakage can be prevented moreeffectively. As the mold release agent described above, it is preferableto use a silicone-based agent. Table 1 shows an example of a compositionof a silicone-based mold release agent. In Table 1, silicone emulsioncontains 40 wt % silicone. The total content of mica and talc is 45 to55 wt %. The preservative and the antifoaming agent are optionallyadded. TABLE 1 (Weight %) Typical Example Range Silicone emulsion 1815-20 Mica (muscovite or 35 30-40 sericite) Talc 15 10-20 Thickener 0.20.1-0.4 (carboxymethyl cellulose) Preservative 0.2 0.1-0.4 Antifoamingagent 0.01 0.01-0.02 (silicone-based) Water remainder remainder

Although the preferred embodiment of the present invention has beendescribed in detail above, it should be understood that variousmodifications, replacements, and substitutions can be made withoutdeparting from the spirit and the scope of the present invention asdefined by the appended claims.

EXAMPLES

Pneumatic tires of a conventional example, examples 1 and 2, andcomparative examples 1 to 3 having the same size of 205/65R15 wereproduced. In the pneumatic tire of the conventional example, a sealantwas applied to an area of an inner surface of the tire corresponding toa tread portion as a puncture prevention layer. In each of the pneumatictires of the examples 1 and 2 and the comparative examples 1 to 3, arubber-like thin-film composed of a latex dry thin-film was disposed asa puncture prevention layer in an area of an inner surface of the tirecorresponding to a tread portion.

In the conventional example, a thickness of the sealant includingpolyisobutylene blended with polybuten was 4 mm. In the examples 1 and 2and the comparative examples 1 to 3, the rubber-like thin-films with athickness of 1.0 mm were formed of natural rubber latex and liquidisoprene rubber latex in various blending ratios.

For each of these test tires, a weight of the sealant or the rubber-likethin-film disposed on the inner surface of the tire was measured, andsealability was evaluated. Table 2 shows the results. The results of theweight measured are indicated by indices based on the weight of theconventional example set to 100. A smaller index means that the tire islighter. The sealability was evaluated by use of ten tires for each ofthe cases where a N65 nail specified by JIS penetrates the tread portionof each tire and where a screw with a diameter of 4.5 mm penetrates thetread portion of each tire. In the former case, an initial internalpressure of each tire was set to 200 kPa, and the N65 nail was allowedto penetrate the tread portion of the tire and then removed. After thetire was left for 24 hours, and the internal pressure of the tire wasmeasured again. In the latter case, an initial internal pressure of eachtire was set to 200 kPa, and the screw was allowed to penetrate thetread portion of the tire and then removed. After the tire was left for24 hours, the internal pressure of the tire was measured again. Ineither case, tires of which internal pressure was maintained at 95% ormore of the initial internal pressure were passed. The evaluationresults show the number of tires passed. TABLE 2 Conventional ExampleExample Comparative Comparative Comparative Example 1 2 Example 1Example 2 Example 3 Puncture sealant rubber- rubber- rubber-likerubber-like rubber-like prevention layer like like thin-film thin-filmthin-film thin- thin- film film NR latex (wt %) — 80 50 100 90 40 LiquidIR latex — 20 50 0 10 60 (wt %) Thickness (mm) 4 1 1 1 1 1 Braking —1080 1080 1050 1100 920 elongation (%) Tensile strength — 16.8 15.9 17.517.0 14.2 (MPa) Sealability N65 10/10 10/10 10/10 10/10 10/10 10/10 nailscrew 10/10  9/10 10/10  4/10  6/10  3/10 Weight (index) 100 82 82 82 8282

As is clear from Table 2, the pneumatic tires of the examples 1 and 2have a puncture prevention function as excellent as that of theconventional example and have a smaller increase in weight. On the otherhand, the puncture prevention function of the pneumatic tires of thecomparative examples 1 and 2 does not work adequately when the screwspenetrate. Examination of the cause thereof reveals that adhesion of therubber-like thin-films to the screws is insufficient. Moreover, thepuncture prevention function of the pneumatic tire of the comparativeexample 3 does not work adequately when the screw penetrates.Examination of the cause thereof reveals inadequate formation of a ballcovering a puncture hole when the screw is removed.

INDUSTRIAL APPLICABILITY

The present invention can be effectively utilized in tire manufacturingindustries and thus in automobile manufacturing industries.

1. A pneumatic tire, comprising: a rubber-like thin-film disposed on aninner surface of the tire, the rubber-like thin-film being formed of alatex dry thin-film in which 20 to 50 wt % rubber component is liquidisoprene rubber and having a breaking elongation of not less than 900%and a tensile strength of not lower than 15 MPa.
 2. The pneumatic tireaccording to claim 1, wherein a thickness of the rubber-like thin-filmis not more than 2.0 mm.
 3. The pneumatic tire according to claim 1,wherein a molecular weight range of the liquid isoprene rubber is 20,000to 40,000.
 4. The pneumatic tire according to claim 1, wherein a moldrelease agent is interposed between the rubber-like thin-film and theinner surface of the tire.
 5. A method of manufacturing a pneumatic tireincluding a rubber-like thin-film on an inner surface of the tire, therubber-like thin-film having a breaking elongation of not less than 900%and a tensile strength of not lower than 15 MPa, the method comprising:poring latex in which 20 to 50 wt % rubber component is liquid isoprenerubber into the tire vulcanized; and drying the latex while rotating thetire to form the rubber-like thin-film composed of a dry thin-film ofthe latex on the inner surface of the tire.
 6. The method ofmanufacturing a pneumatic tire according to claim 5, wherein a thicknessof the rubber-like thin-film is not more than 2.0 mm.
 7. The method ofmanufacturing a pneumatic tire according to claim 5, wherein a molecularweight range of the liquid isoprene rubber is 20,000 to 40,000.
 8. Themethod of manufacturing a pneumatic tire according to claim 5, wherein amold release agent is interposed between the rubber-like thin-film andthe inner surface of the tire.